1.
x^2+x-1=0 可得 x^2=1-x
x^3+2x^2+3=x^3-1+2x^2+4=(x-1)(x^2+x-1+2)+2x^2+4
=2(x-1)+2x^2+4=2x^2+2x-2+4
=4
2.(a-2b+3c)(a+2b-3c)=(a)^2-(2b-3c)^2=a^2-4b^2+12bc-9c^2
3.(x+y)(x^2-xy+y^2)=x^3+y^3
4.(x-y)(x^2+xy+y^2)=x^3-y^3
5.x(x+1)(x+2)(x+3)=x^4+6x^3+11x^2+6x
6.已知a≠b,且a(a+2)=b(b+2）,求a+b的值.
拆开,分解因式得2（a-b）=-(a-b)(a+b)
a+b=-2